Diet and reproductive success of an Arctic generalist predator: Interplay between variations in prey abundance, nest site location, and intraguild predation

Abstract

ABSTRACT Under varying prey abundance, generalist consumers should be less affected than specialists due to their more diverse diet. Nonetheless, when prey availability declines, interspecific competition among consumers should increase and could lead to increased intraguild predation. We examined these potential effects in a generalist predator of the tundra, the Glaucous Gull (Larus hyperboreus), over a 7-yr period characterized by large fluctuations in lemming abundance, a potential prey item for gulls. We studied diet by analyzing regurgitated pellets collected at nests and blood nitrogen and carbon stable isotopes, and we monitored annual nesting density and reproductive success on Bylot Island, Nunavut, Canada. Stable isotopes revealed a relatively similar contribution of terrestrial and marine food sources to the gull diet, although the terrestrial contribution increased in the year of high lemming abundance. According to analysis of pellets, diet during incubation was dominated by geese and lemmin...